It's counterintuitive, you might think "behave yourself" is code for "hahaha I am dumping my problems on you for the afternoon, sucka!". But it really means the parents show some slight awareness about manners and their spawn is likely to be somewhat tame.
I mean kids are still kids, even with the best of intentions they might accidentally drop a slice of cake on the floor etc.
| < seriously, it's nap time | Windows > |

